I'm of the opinion that supermarket fuel (diesel in particular) is the same as branded fuel. I've never had any reason to think otherwise but i'm looking for opinions. I'm not talking about 95RON vs. 98RON or anything, i'm just comparing bog standard petrol/diesel from say, Morrisons, to Shell.

The main argument boils down to the blend of additives in the different fuels from different places. Supermarket fuel normally has more additive in it vs that of branded fuel but it doesn't necessarily make any difference to performance or economy.

I uaually buy branded fuel - not necessarily because I expect better mpg but more for fuel quality/pureness/quality control.
I sometimes use supermarket stuff if I get stuck.
Supermarket diesel may have more 'biodiesel' content (%) which is another reason I am cautious.

So even with BP low sulphur diesel you are getting up to 10% 'biodiesel - I have seen posts by people with their own fuel testers who claim to have seen up to 18% biodiesel in some unbranded fuels (no names)

Edit - this info may be a little out of date but branded fuel should have less than 5% biodiesel in 'normal. diesel.

All fuels are the same until the point they are put into road tankers. That's where the cocktail of additives is blended in to make the branded version. Tesco Momentum has higher levels of ethanol which gives a higher octane rating. Blending rates of biodiesel are I believe generally higher in supermarket fuels.

An RAC man was once recovering diesel Ford Focus in my street. Blocked fuel filter was the diagnosis, regular problem on cars run on supermarket fuel he said. Ford garages always busy with replacing the filters......

I generally use Shell V-Power, but the price premium is bigger than it used to be

Just to add my two cents on this discussion I have used Tesco Momentum, Shell Premium and Costco Premium.
I have found that for a full tank I recieve more mpg from Costco and also the engine seems smoother especially in idle, I did over a 1000 mile in a week a fortnight ago and this was all on Costco fuel and did involve some “spirited” driving.

I agree with just about everything you said TT, people generally don't appreciate the importance of the "fluffy" optional add ons as you call them.

Bullet point 4 would be that fuels have to meet BS EN 228 for petrol or BS EN 590 for diesel. These standard have been updated to allow up to 7% biodiesel by volume and 10% ethanol by volume. (used to be 5% only)

Fuel suppliers under the RTFO have to blend to achieve their legal obligations. It gets (very) complicated when you start allowing for the different weightings for different biomass feedstocks and different blends for summer and winter, but I think the overall minimum blend rate for 2016-17 for ethanol is 4.94% by volume, but it will be rising to 9.75% by 2020.

Ironically, the pioneers of bio-ethanol content was not any of the major oil companies. It was actually a small independent UK oil company by the name of Greenergy. They were original suppliers to Tesco, and developed their original 98 RON Tesco juice (I think it was called Optimax). Tesco then bought a major stake in Greenergy, and they then went on to develop the first 99 RON fuel in the UK - Tesco Momentum. Greenergy had about an 8 year head-start with bio-ethanol content in fuel over the likes of Shell, BP, Esso, etc.

Sadly, Tesco tightened the purse strings on Greenergys R&D, and so whilst Tesco Momentum 99 still provides the highest power output in clean engines compared to Shell V-Power (the only other 99 RON brew in the UK), the additive packages in Greenergy/Tesco fuels have not kept up with the likes of the majors.

The other issue is that it is a simple fact that Momentum / V-Power are totally pointless, unless your engine specifically requires 98 RON 'super plus' unleaded. If you choose to use Momentum simply due to its 'better' additive package over standard Tesco 95 unleaded, you are misguided. The 'base' additive packs in branded 95 unleaded from Esso, Shell, BP, Gulf, Elf, etc are all better than Momentum.

I know Greenergy quite well, initially they simply blended fuels, and over time have moved into biofuel manufacture, sourcing the biodiesel and ethanol from other independent firms (as do all the "big oil" companies). Some are in the UK, others elsewhere in Europe and Brazil. Greenergy actually have around 35% of the UK fuel market these days.

Optimax was actually a Shell petrol product, rebranded a number of years ago as V-Power, the branding now extends to a diesel product. Here in the UK I believe that V-Power is only 98 octane, rather than 99 of Momentum, but on mainland Europe V-Power is a 100 RON product (or at least it used to be).

You are of course correct on the octane requirement, virtually every race car running a custom map in the UK is set up to run on V-Power rather than Momentum (excluding cars set up to run on race fuels where their use is permitted under MSA / FIA rules). When you have seen stripped engines you understand why.

I have been trying to find percentages of 'biodiesel' in different brands of Diesel fuel - No luck with that - but found this BP info..

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So even with BP low sulphur diesel you are getting up to 10% 'biodiesel - I have seen posts by people with their own fuel testers who claim to have seen up to 18% biodiesel in some unbranded fuels (no names)

Edit - this info may be a little out of date but branded fuel should have less than 5% biodiesel in 'normal. diesel.

I realised my Optimax mistake shortly after posting! Before Tescos 99 brew was given the Momentum moniker, it was just called 'Tesco 99' - imaginative, eh?

Crucial aspect of ethanol supply and inclusion - it must be from a biological (plant) source, rather than the traditional fossil fuel distillate. It is the whole 'bio' shebang ethic which is mandated in UK and EU fuels.

V-Power in the UK is 99. Its older defunct Optimax was 98. Does BP still supply their Ultimate 106 RON??

In Germany, many of their super plus unleaded are 100 RON - Shell V-Power and Aral (who are owned by BP) are definitely 100. Can't remember much about other German brands. In Italy, V-Power is still 98 - if you can actually find it!

Our Polo 1.4 16v was designed for 98 fuel,we can just about get away with good quality 95 but she does 'pink' on cheap 95 (I am going to replace the oil separator to reduce the pinking),nowadays we usually just put in tesco 99 whenever we are near a tesco station,the polo seems to run ok on it so far